Lighting and bats: applying the ILP and BCT guidance

Lighting a bat roost access point can be an offence, which is why a lighting scheme on a site with bats is a licensing document as much as a design one. Regulation 43 of the Conservation of Habitats and Species Regulations 2017 makes it an offence to deliberately disturb a European protected species or to damage or destroy a breeding site or resting place, and case handling treats a roost rendered unusable by light as falling within that. The joint Institution of Lighting Professionals and Bat Conservation Trust guidance, Guidance Note 08/23, is the document reviewers expect the scheme to have been designed against.

Why lighting is a licensing question, not only a design one

Two regimes sit behind every lighting condition on a site with bats.

Species protection comes from section 9 of the Wildlife and Countryside Act 1981 and, more relevantly for bats, from the 2017 Regulations. Where a proposal would disturb bats or make a roost unavailable, the work needs a European protected species mitigation licence from Natural England, and the lighting design forms part of the mitigation the licence is granted on. Planning permission does not cure the offence, and a condition requiring a lighting scheme to be submitted later does not either.

The obtrusive light regime is separate. The Institution of Lighting Professionals guidance on the reduction of obtrusive light sets environmental zones from E0, intrinsically dark areas, through to E4, and gives limits for spill, luminance and upward light. Councils increasingly attach conditions in those terms because they are measurable. An ecology led design and an obtrusive light led design usually converge, but they are checked by different people, so state both in the same document.

The practical consequence for a reviewer is sequencing. The lighting design has to be settled before the licence application is submitted, not after the permission is granted, because Natural England will want to see the illuminance at each feature it is asked to accept.

Identifying roosts, access points and commuting routes

A lighting scheme cannot be assessed against a site plan alone. It needs the ecological baseline mapped onto the same drawing.

Three categories of feature matter. Roosts and their access points, which are usually specific: a gap under a ridge tile, a lifted lead flashing, a cavity behind a barge board, a knothole at a stated height on a stated elevation. Commuting routes, typically hedgerows, treelines, walls, ditches and watercourses that bats follow between roost and foraging ground. And foraging areas, which are broader: woodland edge, unimproved grassland, water bodies, mature parkland.

Emergence and re-entry survey results give the access points and the flight lines, and those results come from a licensed ecologist. A Protected Species Survey is one of the report types where a licensed ecologist is legally required, because handling and disturbance need a licence under the 1981 Act and the 2017 Regulations. A draft cannot substitute for the survey, and no lighting design should be finalised without it.

Species identity changes the answer. Horseshoe bats, Myotis species and long-eared bats are strongly light averse and slow flying, and will abandon a lit route rather than cross it. Some pipistrelles and noctules are more tolerant and will feed at lit insect concentrations, though that tolerance carries its own cost in predation risk. Do not design to the tolerance of the least sensitive species recorded.

The detail of how spill interacts with flight behaviour is covered in light spill onto bat commuting and foraging routes, and the survey groundwork sits in the Preliminary Ecological Appraisal and the Bat Survey.

Spectral output and colour temperature

Blue rich white light is the problem. Short wavelength content attracts insects, which draws bats into lit areas, and it is the part of the spectrum to which light averse species respond most strongly.

The design response is a warm source with minimal output below about 500 nanometres and no ultraviolet. Correlated colour temperature of 2700 K or lower is the common starting point, with 2200 K amber used where the sensitivity of the feature justifies it, and narrow band amber or red where the highway authority will accept it. Specify the source by its spectral power distribution where the manufacturer publishes one, not by colour temperature alone, because two sources at the same nominal temperature can differ in their short wavelength content.

Metal halide and older discharge sources are out, and so are any luminaires with an ultraviolet component. Modern LED units make this straightforward, which means the argument with the client is usually about the appearance of amber light rather than about availability.

Optics, mounting height and spill control

Getting light only where it is needed does more than reducing the lumen output.

Vertical illuminance at the feature is the number that matters, not horizontal illuminance on the ground. Guidance Note 08/23 does not set one universal threshold for every situation, and practice commonly works to a maximum of around 1 lux at the dark feature, with a lower figure where the species present are particularly sensitive. Agree the target with the ecologist and record the agreed figure in the assessment rather than importing a number from another scheme.

Watch the sources that never appear in a lighting drawing. Vehicle headlights sweeping a boundary as cars turn, illuminated signage, bollard lights in landscaping packages, security floodlights fitted by occupiers after handover, and glazing spill from large windows all light features that the scheme shows as dark. Headlight spill in particular is often the largest single contributor on a residential layout, and the answer is usually a landscape one: a dense hedge or a bund on the corridor side.

Part night operation and curfews

Dimming and curfews carry real weight, because they remove the light during the hours that matter most.

Bats emerge around dusk and return before dawn, with activity concentrated in the first couple of hours after sunset in the warmer months. A curfew that switches off amenity and car park lighting after a stated time helps less than a scheme that is dark at emergence. Where operational needs prevent that, dimming profiles that drop output steeply during peak activity are the usable compromise.

On residential sites, passive infrared control with a short timed run-on is worth more than a lower wattage on a permanently lit luminaire. It also removes the argument about security, since the light is there when someone is present.

Set out the control strategy as part of the scheme rather than as an aspiration: which luminaires are on which circuit, what the dimming steps are, what times they change, and how the settings are protected from being overridden by a future managing agent.

Dark corridors and unlit buffers

The strongest measure in most schemes is spatial. A continuous unlit route from roost to foraging ground, following an existing linear feature and buffered from the lit parts of the site, preserves the function of the habitat rather than mitigating its loss.

That means designing the layout around the corridor rather than fitting the corridor into the leftover space. Keep the built edge back from the feature, avoid lit footpaths crossing it, and where a crossing is unavoidable use a dark gap with shielded, low level, warm lighting either side rather than continuous illumination. The design approach is set out in designing a dark corridor for bats across a site.

Long term protection matters as much as the initial design. A corridor with no management plan and no ownership becomes a lit alleyway within five years, so tie it to a management regime and, where the scheme is large enough, to a planning obligation.

Evidence the authority and the ecologist both need

A lighting submission that clears both the ecologist and the case officer contains the following, and a reviewer should ask for whatever is missing.

1. A luminaire schedule giving type, wattage, lumen output, correlated colour temperature, spectral power distribution where published, optical control, upward light ratio and any accessories fitted.
2. A layout drawing showing column positions, mounting heights, aiming and the ecological features overlaid.
3. Isolux contours in plan at ground level, plus vertical illuminance values at each roost access point, commuting route and foraging feature, with the agreed target stated.
4. The control strategy, with circuits, dimming profile and switching times.
5. An assessment against the obtrusive light environmental zone the authority has applied, covering spill, upward light and glare.
6. A statement of the residual effect, and where relevant the licensing position with Natural England.
7. A commitment to a post installation verification survey, so the built scheme is checked against the approved one.

PlanScope drafts a Lighting Assessment structured to the standards councils cite, with site measurements and survey results flagged rather than assumed. Councils normally expect a suitably qualified lighting designer, and bat survey work must come from a licensed ecologist, so treat the draft as the framework those professionals complete. Reports should be reviewed before submission, and PlanScope does not guarantee planning approval. For specialist technical reports, qualified professional input may be required.

This is general guidance, not legal advice. Check the current guidance and licensing position with Natural England, your local planning authority and a licensed ecologist before relying on it.